The present invention relates to an apparatus and a method for transmitting a quadrature modulated signal, and an apparatus and a method for receiving the quadrature modulated signal. More particularly, the present invention relates to an apparatus and a method for transmission, an apparatus and a method for reception, and an apparatus and a method for transmission and reception, all of which enable reliable adaptive equalization on the receiving side in transmission and reception in a millimeter wave band.
Conventionally, there has been technology for wireless LANs (Local Area Networks), which constructs a LAN by communication using radio waves and infrared rays. A wireless LAN uses radio waves in a quasi-microwave band, for example a 2.4 GHz frequency band, to achieve a communication speed of 1 to 2 Mbps. Recently, communication over a wireless LAN using a higher frequency band, for example a 60 GHz band, has been proposed. Use of radio waves in such a millimeter wave band makes it possible to achieve a higher communication speed.
Multipath interference tends to occur in communication using radio waves in such a millimeter wave band. When there is multipath interference, characteristics of a communication channel are changed with time as the receiving side or the transmitting side is moved, for example. In addition, in communication using radio waves in a millimeter wave band, a slight movement of the receiving side and the transmitting side may result in a change in phase. Therefore, an equalizer on the receiving side needs to equalize a signal adaptively.
Conventionally, a training time is provided by time division during communication, and known data is transmitted as a pilot signal during the training time. A coefficient of an equalizer on the receiving side is renewed on the basis of the pilot signal, and after the coefficient converges, the coefficient of the equalizer is fixed to transmit data. According to this method, if a sufficient time period and frequency band for transmitting the pilot signal are not secured, in a case where characteristics of the communication channel are changed with time, adjustment of the coefficient of the equalizer cannot track the changes in the characteristics of the communication channel, thus resulting in degraded characteristics of the equalizer with respect to received radio waves.
On the other hand, a method has been used which renews the coefficient of the equalizer on the basis of known data transmitted during a training time, makes data determination during a tracking time after convergence of the coefficient, and uses the data as known data for adjustment of the coefficient of the equalizer. According to this method, the characteristics of the equalizer with respect to received radio waves are degraded when there is an error in the data determination.
In this case, when an IIR type filter is used for the equalizer, in particular, the characteristics of the equalizer are degraded, and also the equalizer may diverge.